Johnson, 29, was in the Eastern Regional Jail in April 1997 awaiting trial for kidnapping, attempted murder and other charges when a 20-year-old inmate accused him of rape.
On Tuesday, the victim, who was in the prison on a charge of possession of a stolen vehicle, testified Tuesday that Johnson used to play "games" with him, making sexually suggestive comments.
He never took him seriously until April 26, after a card game in Johnson's cell, the man testified. Johnson threatened to beat him up and force sex on him if he didn't comply, the man said.
"There was really nothing I could do," the man told the jury. "He stood up and told me to pull down my pants or he would basically knock me out and take it from me."
Afterward, the victim said, Johnson came to his cell and told him it would never happen again and threatened to hurt his parents and girlfriend if he told anyone.
The next night, he played cards with Johnson and others before returning to his cell.
Johnson appeared in the doorway and told the man to come to his cell, the man said. He did, out of fear, and was sodomized again, the man testified.
It wasn't reported to authorities for more than two weeks - when Johnson was moved to a different part of the jail - because the man was fearful of paybacks, according to testimony.
"He didn't tell until he felt it was safe," said Prosecuting Attorney Pamela Games-Neely.
Three other inmates testified Tuesday - one who said he saw the attack and two others who said the victim talked about getting Johnson in trouble with sexual assault allegations.
Kevin Winston, 31, said he walked in on Johnson and the man just prior to one of the acts.
Winston said he went to Johnson's cell to borrow some personal hygiene items. The victim was there and Johnson was being sexually suggestive.
"All the time I didn't take him seriously. I don't think (the victim) did either," Winston said. "The next thing I know, (the victim) dropped his pants."
He said he wasn't in a position to stop it.
"I'm just an inmate, just as well as the next guy," Winston said.
Winston testified against Johnson's ex-girlfriend, Tammy Reel, at a drug trial, and two other inmates said Winston and the victim told them they were going to accuse Johnson of sexual assault to "get him."
Games-Neely asked the jury why someone would go through the hassle of trial and publicity for false allegations.
Johnson is scheduled to be sentenced Friday.
He is serving a life sentence for kidnapping a Gaithersburg, Md., man in August 1996 and dumping his body in the Potomac River because he thought he was dead.
Johnson's court-appointed attorney, David A. Camilletti of Shepherdstown, W.Va., said he will argue for acquittal and a new trial at the sentencing.